Or the several versions of Invasion of the Body Snatchers, of which I count about five movies . . . and, perhaps, many more if we broaden the category a bit.
I was surprised to find out that this whole sub-genre of science fiction is an extremely common motif and is–perhaps–based on Capgras Syndrome or–in older literature–Capgras delusion.
This syndrome can happen if someone develops a leision on a specific portion of the brain, as might happen with a head injury, poisoning (as with some types of long-term heavy metal poisoning, and I don’t mean one of my preferred musical genre), electrocution, prenatal exposure to meth and PCP, and so on.
In Capgras, the sufferer becomes convinced that everyone around them has been replaced by imposters, and that there is a conspiracy . . . usually by the co-ordinated work of a unified enemy that is systematically replacing all of their friends and loved ones.
Added later: There does seem to be some unverified story that a young man hated his parents so much that he was happy when he developed Capgras, as hostile aliens (or spirits, djinn, etc.) were an improvement over his abusive parents.
In fairness, this story seems plausible on the surface, but I really, really think that this story is complete and utter bullshit.
I only mention this last nuance (“abusive parents”) to let my readers know that I am aware of this, and–based on 35 years of experience in the medical field–I honestly believe that this story is bullshit.
Please don’t lend any credibility to such stories without vetting the source.
Despite this, a cool rumor . . . huh?